Examples of systems for computer trading of interests are disclosed in U.S. patent applications Ser. No. 09/584,045, filed 30 May 2000 and entitled ELECTRONIC TRADING SYSTEM FOR ELECTRICITY FORWARDS; Ser. No. 09/839,529, filed 20 Apr. 2001 and entitled PRICE CHANGE OF ORDERS FROM RESERVE IN AN ELECTRONIC TRADING SYSTEM; and Ser. No. 10/395,839, filed 24 Mar. 2003 and entitled VARIABLE PRICING FOR AND CONDITIONAL AVAILABILITY OF PROPOSALS FOR TRADING OF FINANCIAL INTERESTS; the entire disclosure of each of which is hereby incorporated herein by this reference.